Loudspeaker broadcasts music by generating vibration through a diaphragm at corresponding amplitudes according to audio signals. It allows people to enjoy music anytime anywhere. Advance of technology enables the loudspeaker to be made in a compact size and portable to facilitate carrying outdoors so that people can enjoy music outside the houses or during recreation. However, the conventional portable loudspeakers mostly focus on microminiaturization that compromises acoustic quality.
The diaphragm is vibrated to generate sound waves. Forward resonance sound waves are generated when the diaphragm is vibrated forwards, and reverse resonance sound waves are generated when the diaphragm is vibrated rearwards. Most conventional portable loudspeakers at present have only one audio outlet for output of the forward resonance sound waves. They usually do not have sound channel structure, hence a great portion of the forward resonance sound waves are muffled in the portable loudspeaker. This causes loss of bass broadcasting. Hence the portable loudspeaker often provides only treble output but does not generate bass resonance, and results in inferior sound quality. For instance, R.O.C. utility model No. M343997 discloses a speaker in which the reverse resonance sound waves are generated and muffled in the resonance cabinet so that sound cannot be output effectively to result in poor sound quality. Another R.O.C. utility model No. 467461 discloses a mini sound cabinet equipped with a sound channel structure. It has a sound channel tube and a sound channel trough to transmit and broadcast bass. But its sound channel structure is fixed and cannot be changed. It also is quite bulky and difficult to carry or be packaged for transportation. To provide structural improvement for the portable loudspeaker to output the bass effectively can help to improve the acoustic quality of the portable loudspeaker.